This invention relates to concrete with improved freeze/thaw tolerance, and more particularly to such concrete in which crumb rubber replaces some or all entrained air ordinarily incorporated to enhance freeze/thaw tolerance.
The concrete mixing and placing process will inevitably make some air voids entrapped in concrete. Typically, the content for those entrapped air voids in concrete is about 1% to 3% in terms of total concrete volume. However, building concrete outdoor structures in a cold climate typically requires a design of 5% air content or more in concrete for the purpose of increasing concrete""s ability to resist freeze/thaw damage. The increase in air content can be achieved by adding an additive called air entraining agent (AEA). So, after AEA is added, concrete has both entrapped air voids and entrained air voids. The manufacturers of AEA will label the amount needed to yield a given percentage of entrained air for one cubic yard of concrete. This is a simple design routine.
At the same time, however, AEA weakens concrete, and compensation is needed. More cement is put into concrete for this purpose to make concrete xe2x80x9cstronger.xe2x80x9d This drives cost up since cement is the most expensive ingredient in concrete.
There remains, therefore, the need for a concrete with the ability to resist freeze/thaw damage, but without the attendant increase in cost that the addition of air entrainment agents and additional cement bring.
In accordance with this invention, in concrete designed for use in locales where repeated freezing and thawing occurs, crumb rubber is added to the mix while air entrainment agents are reduced or eliminated so that entrained air is reduced or eliminated. The increase in cement and its attendant cost increase can be eliminated while a concrete with improved freeze/thaw tolerance is nevertheless produced.
In a method of making the concrete in accordance with this invention the percentage of air in air entrained concrete is conventionally determined for the anticipated freeze/thaw conditions to be tolerated and depending upon the percentage of air, the amount of crumb rubber content is arrived at for a crumb rubber concrete having the desired tolerance to the predetermined freeze/thaw conditions.
In a further embodiment of the invention, the crumb rubber replaces all of the entrained air that ordinarily would be brought into the mix by the air entrainment agent.
A concrete with designed 3000 psi 28-day compressive strength in a cold climate in accordance with this invention comprises, per cubic yard, 350 to 425 lbs. of cement, 0 to 100 lbs. of fly ash, 170 to 300 lbs. water, 1000 to 1500 lbs. of sand, 1100 to 1900 lbs. of coarse aggregate, 0% to 4% air and 5 to 32 lbs. of crumb rubber, and other appropriate amounts of additives excluding an air entraining agent.
The above and further objects and advantages of the invention will be better understood from the following detailed description of at least one preferred embodiment of the invention, taken in consideration with the accompanying drawings.